Flame retardant composition

ABSTRACT

SELF-EXTINGUISHING PLASTIC MATERIALS ARE PREPARED BY INCORPORATING IN THE PLASTIC A COMPOSITION OF AN ORGANIC BROMINE COMPOUND, AN ORGANIC PHOSPHATE AND A LEAD SALT.

United States Patent 3,829,394 FLAME RETARDANT COMPOSITION Maria Feiner,Henin Lietard, Michel Gubler, Paris, and

Joseph Guillon, Meurchin, France, assignors to Monsanto Company, St.Louis, M0.

N0 Drawing. Original application Sept. 10, 1 970, Ser. No. 71,238, nowPatent No. 3,677,942. Divided and this application Mar. 1, 1972, Ser.No. 231,039 Claims priority, application France, Sept. 12, 1969,

6931182 Int. Cl. C09k 3/28 US. Cl. 260-4 AR 10 Claims ABSTRACT OF THEDISCLOSURE Self-extinguishing plastic materials are prepared byincorporating in the plastic a composition of an organic brominecompound, an organic phosphate and a lead salt.

This application is a division of applicants copending application Ser.No. 71,238, filed Sept. 10, 1970, now US. 3,677,942.

This invention relates to a flame-retardant formulation and topolyvinylaromatic resin composition incorporating such a flame-retardantformulation.

Vinylaromatic polymers are an important industrial commodity finding awide range of applications in many diverse fields. It has been observed,however, that such vinylaromatic polymers are often flammable and inconsequence, in applications where there is a fire risk, such as forexample in electrical appliances and in the building industry, a demandhas grown up for self-extinguishing or flame-retardant grades of thesepolymers. Indeed, in some countries regulations are in force whichrequire the use of self-extinguishing grades of all plastics used in thebuilding industry. It is found, however, that the incorporation offlame-retardant additives often has undesirable side effects, such asfor example corrosion of the processing machinery as a result ofpremature decomposition of the additive. It is also possible for suchadditives deleteriously to affect the physical properties of thepolymer.

Accordingly, the present invention comprises a flameretardantformulation comprising (a) either a brominesubstituted hydrocarbonhaving from 2 to 4 carbon atoms and at least 4 bromine atoms in themolecule, or a bromine-substituted phenol having from 2 to 5 bromineatoms in the aromatic nucleus; (b) a tris(bromoalkyl) phosphate whereinthe bromoalkyl groups comprise from 2 to 5 carbon atoms and at least 2bromine atoms; and (c) a lead salt. Other components can of course bepresent.

The bromine-substituted hydrocarbon can be for example acetylenetetrabromide; 1,2,2,3-tetrabromopropane; 1,1,2,3,4-pentabromobutane or1,1,2,2,4,4-hexabromobutane. However, the preferred bromine-substitutedhydrocarbons are bromine substituted ethanes and propanes and especiallyacetylene tetrabromide.

Suitable bromine-substituted phenols include for example2,4-dibromophenol; 2,4,6-tribromophenol and pentabromophenol. Thepreferred phenols are, however, those having 4 or 5 bromine substituentsand of these the most preferred is pentabromophenol.

The tris(bromoalkyl) phosphate component of the mixture is one in whichthe bromo-alkyl group contains from 2 to 5 carbon atoms and at least 2bromine atoms. Examples of suitable bromoalkyl groups that can bepresent in the phosphate include 1,2-dibromoethyl; 2,3-dibromopropyl;2,3,4-tribromobutyl and 2,2,3,4-tetrabromopentyl. It is preferred,however, that the bromoalkyl group present contains 2 or 3 carbon atomsand 2 bromine atoms. In practice excellent results have been obtained byusing tris(2,3-dibromopropyl) phosphate.

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Thus the preferred flame-retardant formulations of the inventioncomprise (a) acetylene tetrabromide or pentabromophenol, (b)tris(2,3-dibromopropyl) phosphate, and (c) a lead salt.

The amount of the bromine-substituted hydrocarbon or phenol present inthe formulation can represent for example from 40 to 60 percent of thetotal weight of the formulation. However, the preferred amount ofbromine-substituted hydrocarbon lies in the lower part of the aboverange, that is to say from 40 to 50 percent by weight of theformulation. By contrast the preferred amount of bromine-substitutedphenol lies in the higher part of the above range and especially from 50to 60 percent of the total weight of the formulation.

The tris(bromoalkyl) phosphate can conveniently be present in theformulation in a percentage of, for example from 30 to 60 percent byweight but in general the formu lation comprises from 35 to 55 percentand particularly from 40 to 50 percent by weight of the phosphate.

The amount of lead salt in the formulation often represents from 0.5 to12 percent by weight of the formulation, but in general, satisfactoryformulations of the invention comprise a lead salt in a proportion offrom 1 to 10 percent and particularly from 1 to 8 percent by weight.

The lead salt is most suitably a basic salt that is to say one in whicheach molecule of the salt is associated with one or more molecules oflead oxide or lead hydroxide. Thus, the lead salt can be a basic form ofa salt such as lead carbonate, lead sulphate, lead silicate, leadstearate or lead phthalate. Particularly preferred among these aretribasic lead sulphate, dibasic lead stearate and monobasic leadste-arate. The lead salt component of the formulation can of coursecomprise a mixture of such salts and in fact a preferred compositioncomprises a mixture of tribasic lead sulphate and dibasic lead stearatein which the ratio of tribasic lead sulphate to dibasic lead stearate isfrom 9:1 to 2:1 and especially about 4: 1.

The invention also comprises a polyvinylaromatic resin compositioncomprising the flame-retardant formulation described above. The amountof flame-retardant added to the polyvinylaromatic resin depends to someextent on the degree of flame-retardance required and the constituentsof the flame-retardant additive, however, it is found that efficientflame-retardance is obtained when the resultant proportion by weight ofbromine in the resin composition is from 1.5 to 2.0% and especially from1.6 to 1.8%.

The vinylaromatic polymer is a homopolymer or copolymer of avinylaromatic monomer, such as for example styrene, a chlorostyrene, avinyl toluene, or a-methyl styrene. A copolymer can be one of avinylaromatic monomer with other olefinic monomer, for exampleacrylonitrile, vinyl chloride, vinyl acetate, methyl acrylate, methylmethacrylate, or ethyl acrylate. It can also be a graft copolymer of oneor more monomers on to a polymer, for example a graft of styrene andacrylonitrile on to a natural or synthetic rubber such as apo'lybutadiene. Those acrylonitrile '(butadiene) styrene resins known asABS are particularly suitable. The acrylonitrile, butadiene or styrenecan if desired be wholly or partially replaced by a homologue, forexample methacrylonitrile, isoprene and a-methylstyrene or vinyltoluenerespectively. Toughened polystyrenes can be employed, for instance onethat has been obtained by modification before or after polymerizationwith a natural or synthetic rubber especially polybutadiene. Excellentresults have been obtained using homopolystyrene or more preferably atoughened polystyrene of the type described above.

The composition may further comprise an antioxidant to retarddegradation of the material during fabrication and during exposure tooxidizing conditions while in use. Typical among the many suitableantioxidants which can be employed are alkylated phenols, such as forexample '2,6-ditertiarybutyl-p-cresol. Where such an antioxidant is usedit is usually found sufficient to add up to one part, for example from.1 to .5 part by weight of antioxidant for every 100'parts'by weight ofth'polyvinylaromatie resin.

Other additivessuch asfor example mold release agents, flow improvers,light stabilizers, slip additives and antistatic additives can also bepresent if desired.

Where the composition comprises a substance such as acetylenetetrabromide that is a'liq'uid at room temperature, it is found that theincorporation of the additives into the polymer can best be accomplishedby absorbing the substance on to finely divided silica and incorporatinga master-batch of the additives into the polyvinylaromatic resin. If,however, only substances that are solid at room temperature are used, itis possible to dispense with the silica.

The invention is further illustrated by the following examples.

EXAMPLE 1 This example compares a self-extinguishing grade of rubbermodified polystyrene prepared according to the invention with a similarbut non-self-extinguishing grade of rubber modified polystyrene.

A rubber-modified polystyrene, comprising 2.4% by weight of rubber, wasdivided into the samples.

One sample was made self-extinguishing by incorporating into it theadditives shown below and the other sample was retained as a blank.

Percent Tris(2,3-dibromopropyl) phosphate 1 Pentabromophenol 1.35Tribasic lead sulphate 0.03 Dibasic lead sulphate 0.0072,6-Ditertiarybutyl-4-methyl-phenol 0.3

all proportions being by weight of the sample. The samples were extrudedthrough a 150 mm. diameter extruder at 240 to 250 C. without trouble.

The properties of the self-extinguishing composition formulatedaccording to the invention as shown above were compared with those ofthe blank and the results of the tests are shown below.

Self-extinguishing composition Blank 1 Tensile strength at yield (p.s.i4,165 3, 640 2 Tensile strength at fail (p.s.i.) 4, 525 4,030 3Elongation at failure (percent 29 24. 4 Izod impact strength (it.lb./in) 0. 60 0.61 5 Heat distortion C.) 72.5 73 6 Burning rate(cm./min.) 3.5 7 Extinction time (see) 8 8 Extent of burning (mm.)- 3. 5Total 9 Injection temperature, C 190 200 1 Self-extinguishing. 2 Burned.

The example compares a self-extinguishing grade of rubber-modifiedpolystyrene prepared according to the invention, using acetylenetetra-bromide, with a similar but non-self-extinguishing rubber modifiedpolystyrene.

A master-batch identical to the one described in Example 1 was preparedand divided into two samples. One

was kept as a blank and to the other was added the following:

Percent Acetylene tetrabromide 1 Tris(2,3-dibromopropyl) phosphate 1Silica (as a base on which the acetylene tetrabromide was absorbed) 0.4Tribasic lead sulphate 0.112 Dibasic lead stearate 0.028 Monobasic leadstearate 0.010 *Magnesium stearate x 0.2

all proportions being by weight of the sample. N I

The properties of the two samples were thenevaluated using test methodsdescribed in Example 1, with the following results:

Self-extinguishingcomposition Blank 1 Tensile strength at yield (p.s.i.)4, 185 3, 500 2 Tensile strength at failure (p.s.i.) 4, 500 4, 000 3Elongation at failure '23 24 4 Izod impact strength (ft lb 0.64 0. 63 5Heat distortion O.) 74.5 76 6 Burning rate (cm./min.).. 3.5 7 Extinctiontime (see)- 5 8 Extent of burning (mm.) 10 Total 9 Injection temperatureC.) 180-185 200 1 Non-burning. 2 Burned. 7

Again the physical properties of both formulations were similar but theone prepared according to the invention had excellent flame-retardantproperties.

EXAMPLE 3 This example compares a homopolystyrene composition accordingto the invention with an untreated homopolystyrene.

Two identical samples of homopolystyrene were obtained. One sample wasblended with the following additives: I

Percent Tris(2,3-dibromopropyl) phosphate 1 Pentabromophenol 1.35 Leadsulphate 0.03 Lead stearate 0.007

all percentages being by weight of the polymer.

The other sample was kept as a blank. Both samples were extruded througha 40 mm. diameter extruder at 180200 C.

The blended sample assessed according to the methods used in Example 1had an extinction time of 0.9 sec. and did not burn whereas the blankburned completely.

The physical properties as determined according to the test methodsdescribed in Example 1 are set out in the following table.

Sample prepared according to the invention Blank As before the physicalproperties are not seriously affected but the self-extinguishingcharacter of the resin composition is much improved.

EXAMPLE 4 This example compares self-extinguishing grades ofrubber-modified polystyrene prepared according to the invention, with asimilar rubber-modified polystyrene which does not contain a lead salt.

A rubber-modified polystyrene, comprising 2.4% by weight of rubber wasdivided into three samples.

The following quantities of additives were incorporated in one of thesamples:

Percent Acetylene tetrabromide 1 Tris(2,3-dibromopropyl) phosphate 1Silica (as a base on which the acetylene tetrabromide was absorbed) 0.4

Magnesium stearate 0.2

all proportions being by weight of the sample.

In the remaining samples there was incorporated the above quantities ofthe additives together with various proportions of lead salts, as shownin the Table below.

The samples were extruded through a 40 mm. diameter extruder at 180 C.to 200 C.

The burning temperature was evaluated by noticing the moldingtemperatureat which black burning marks appeared on injection molded plaquesemploying an Arburg Allrounder 200 S molding machine.

It can be seen from the results in the Table that the presence of leadsalts in the compositions of the present invention gives a producthaving improved general properties over the non-lead-salt containingcomposition. The increase in burning temperatures that is due to thepresence of the lead salts represents a significantly improvedcomposition. Slight increases in the values of the extinction time andextent of burning of these compositions do not signify a noticeabledeterioration in these properties and in fact the values shown representexcellent properties.

While this invention has been described with respect to certainembodiments, it is not so limited, and it should be understood thatvariations and modifications may be made which are obvious to thoseskilled in the art without departing from the spirit or scope of theinvention.

We claim:

1. A resin composition comprising a polyvinylaromatic resin and aflame-retardant formulation comprising (a) a bromine-substitutedhydrocarbon having from 2 to 4 carbon atoms and at least 4 bromineatoms, or a bromine-substituted phenol having from 2 to 5 bromine atomsin the aromatic nucleus, (b) a tris(bromoalkyl) phosphate wherein thebromoalkyl groups comprise from 2 to 5 carbon atoms and at least 2bromine atoms, and (c) a lead salt.

2. A resin composition according to Claim 1, in which thepolyvinylaromatic resin is selected from the group consisting of ahomopolymer or copolymer of styrene.

3. A resin composition according to Claim 1, in which the resin is apolystyrene modified before or after polymerization with a natural orsynthetic rubber.

4. A resin composition according to Claim 1, in which the amount offlame-retardant formulation present is sufficient to provide apercentage of bromine in the resin composition of from 1.5 to 2.0%.

5. A resin composition according to Claim 1 which further comprises aphenolic antioxidant.

6. A resin composition according to Claim 5 in which the antioxidant is2,6-ditertiary butyl-p-cresol.

7. A resin composition according to Claim 5 in which there is up to 1part by weight of antioxidant for every 100 parts by weight of thepolyvinylaromatic resin.

8. A resin composition according to Claim 2, in which thepolyvinylaromatic resin is an acrylonitrile/butadiene/ styrene (ABS)resin.

9. An article fabricated from a resin composition according to Claim 1.

10. An article fabricated from a resin composition according to Claim 8.

References Cited UNITED STATES PATENTS 2,610,920 9/1952 Hopkinson 106-152,676,946 4/1954 McCurdy et'al. 26045.75 2,912,397 1 1/ 1959 Honska eta1. 26023 3,058,926 10/1962 Eichhorn 2602.5 3,372,141 3/1968 Dickersonet a1. 260--45.95 3,385,819 5/1968 Gouinlock, Jr. 26045.75 3,418,26312/1968 'Hindersinn et al. 26023 3,420,786 1/1969 Weber et al. 2602.53,445,404 5/ 1969 Ronden et a1 2602.5 3,637,555 1/1972 Marinacci et a1.26023.7 3,639,304 2/1972 Raley, Ir. 26025 OTHER REFERENCES Hilado,Flammability Handbook for Plastics, 1969, pp. and 86.

DONALD E. CZAJA, Primary Examiner R. A. WHITE, Assistant Examiner U.S.Cl. X.R.

26045.7 -P, 45.7 R, 45.75 R, 45.95 H, 45.95 R, 876 R, 880 R, 892

